1. Field of the Invention
The present invention relates to a drive circuit for driving a capacitive electromechanical transducer device and an image display device including the drive circuit, and more particularly to a drive circuit for operating an optical scanning mirror using a capacitive electromechanical transducer device constituted of a plurality of piezoelectric elements or the like and a retina scanning display device (retinal scanning display device) including the drive circuit.
2. Description of the Related Art
Recently, there has been proposed an image display device which allows an optical flux to be incident on a pupil and the incident optical flux to be projected on a retina so that a viewer can observe a virtual image in front of the pupil. That is, there has been proposed a so-called retina scanning device.
This type of retina scanning display device uses an optical flux scanning means for scanning the optical flux in the horizontal direction or in the vertical direction. For example, patent document 1 (JP-A-2005-181477) describes an optical scanner constituted of a capacitive electromechanical transducer device as an optical scanning means.
FIG. 17 shows one example of an optical scanner 200 of a mechanical resonance system constituted of a capacitive electromechanical transducer device. The optical scanner 200 is, for scanning the optical flux direction, configured to oscillate by resonance an oscillatory body 224 which arranges a reflection mirror 220 for reflecting the optical flux and changing the radiation direction of the optical flux therein.
As shown in FIG. 17, the oscillatory body 224 is supported on a fixed frame 216, and includes two piezoelectric elements 250, 252 which are fixed to the oscillatory body 224 and the fixed frame 216 respectively. Here, the piezoelectric elements 250, 252 respectively function as drive sources, and generate torsional oscillations about an oscillation shaft Lr so as to oscillate the reflection mirror 220.
Here, FIG. 18 shows an equivalent circuit of the optical scanner 200 and a drive circuit 270 of the optical scanner 200.
As shown in FIG. 18, the piezoelectric element 250 of the optical scanner 200 can be expressed as a circuit in which a resonance circuit 280 formed by connecting an LM100, a CM100 and an RM100 in series and a capacitor CP100 are connected in parallel to each other. In the same manner, the piezoelectric element 252 of the optical scanner 200 can be expressed as a circuit in which a resonance circuit 282 formed by connecting an LM101, a CM101 and an RM101 in series and a capacitor CP101 are connected in parallel to each other.
Then, the drive circuit 270 inputs a positive-phase sinusoidal signal V+ (=Vo{1+cos(2πft)}) to the piezoelectric element 250 via a transistor Tr100, and inputs a negative-phase sinusoidal signal V− (=Vo{1−cos(2πft)}) to the piezoelectric element 252 via a transistor Tr101.
In this manner, by inputting the two-phase sinusoidal signals having phases different from each other to the piezoelectric elements 250, 252, the driving circuit 270 generates the torsional oscillations in the oscillatory body 224 about the oscillation axis Lr thus oscillating the reflection mirror 220.